One of the most basic forms of a modern telecommunication system comprises a telephone system, allowing two users to establish a voice connection, in order to have a telephone conversation.
This basic telephone system developed over the years, first adding some additional functionality and establishing a billing system that was based for instance upon the duration of the telephone call, and upon the respective location of the caller and the receiver. Later on, further functionalities were added. One of these functionalities was collect calling. In this way, a caller could put the costs of the telephone call to the receiver.
In the early telephone systems, where switching and connection was done manually, it was easy to check and control the connections. In more modern electronic and digital switching centres, it became more and more difficult to check and control the connections. In particular when a call crossed different providers and even borders, it was found complicated or impossible to check the connection. In particular when the caller is not allowed to have telecommunication with certain parties, or is restricted in his or her permission to have telecommunication. This is even more complicated if the receiving party should be billed for, or should be able to accept, the costs for a telecommunication connection with the caller.